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https://www.readbyqxmd.com/read/30333895/terminal-alkenes-from-acrylic-acid-derivatives-via-non-oxidative-enzymatic-decarboxylation-by-ferulic-acid-decarboxylases
#1
Godwin A Aleku, Christoph Prause, Ruth T Bradshaw-Allen, Katharina Plasch, Silvia M Glueck, Samuel S Bailey, Karl A P Payne, David A Parker, Kurt Faber, David Leys
Fungal ferulic acid decarboxylases (FDCs) belong to the UbiD-family of enzymes and catalyse the reversible (de)carboxylation of cinnamic acid derivatives through the use of a prenylated flavin cofactor. The latter is synthesised by the flavin prenyltransferase UbiX. Herein, we demonstrate the applicability of FDC/UbiX expressing cells for both isolated enzyme and whole-cell biocatalysis. FDCs exhibit high activity with total turnover numbers (TTN) of up to 55000 and turnover frequency (TOF) of up to 370 min-1 ...
September 7, 2018: ChemCatChem
https://www.readbyqxmd.com/read/30263084/competitive-adsorption-of-nitrite-and-hydrogen-on-palladium-during-nitrite-hydrogenation
#2
Rolf Sybren Postma, Roger Brunet Espinosa, Leon Lefferts
Nitrite hydrogenation is studied in steady-state as well as transient operation using a Pd catalyst in a tubular membrane contactor reactor. A negative reaction order in hydrogen in steady state operation proofs that hydrogen and nitrite adsorb competitively. In transient operation, feeding nitrite to the Pd surface fully covered with hydrogen results initially in very low conversion of nitrite, speeding up once hydrogen is removed from part of the Pd surface. Additional proof for competitive adsorption between hydrogen and nitrite is provided by the observation that exposure of a nitrite-covered catalyst to hydrogen induces desorption of nitrite...
September 7, 2018: ChemCatChem
https://www.readbyqxmd.com/read/30333894/expansion-of-the-substrate-specificity-of-porcine-kidney-d-amino-acid-oxidase-for-s-stereoselective-oxidation-of-4-cl-benzhydrylamine
#3
Kazuyuki Yasukawa, Fumihiro Motojima, Atsushi Ono, Yasuhisa Asano
Discovery and development of enzymes for the synthesis of chiral amines have been a hot topic for basic and applied aspects of biocatalysts. Based on our X-ray crystallographic analyses of porcine kidney D-amino acid oxidase (pkDAO) and its variants, we rationally designed a new variant that catalyzed the oxidation of ( S )-4-Cl-benzhydrylamine (CBHA) from pkDAO and obtained it by functional high-throughput screening with colorimetric assay. The variant I230A/R283G was constructed from the variant R283G which had completely lost the activity for D-amino acids, further gaining new activity toward ( S )-chiral amines with the bulky substituents...
August 21, 2018: ChemCatChem
https://www.readbyqxmd.com/read/30263083/smart-nanoparticles-for-selective-immobilization-of-acid-phosphatases
#4
Flóra Nagy, Gábor Tasnádi, Diána Balogh-Weiser, Evelin Bell, Mélanie Hall, Kurt Faber, László Poppe
An easy to use method combining the selectivity of metal chelate affinity binding with strong covalent linking was developed for immobilization of non-specific acid phosphatases bearing a His-tag from crude cell lysate. Silica nanoparticles were grafted with aminopropyl functions which were partially transformed further with EDTA dianhydride to chelators. The heterofunctionalized nanoparticles charged with Ni2+ as the most appropriate metal ion were applied as support. First, the His-tagged phosphatases were selectively bound to the metal-chelate functions of the support...
August 21, 2018: ChemCatChem
https://www.readbyqxmd.com/read/30197686/sequence-based-in-silico-discovery-characterisation-and-biocatalytic-application-of-a-set-of-imine-reductases
#5
Stefan Velikogne, Verena Resch, Carina Dertnig, Joerg H Schrittwieser, Wolfgang Kroutil
Imine reductases (IREDs) have recently become a primary focus of research in biocatalysis, complementing other classes of amine-forming enzymes such as transaminases and amine dehydrogenases. Following in the footsteps of other research groups, we have established a set of IRED biocatalysts by sequence-based in silico enzyme discovery. In this study, we present basic characterisation data for these novel IREDs and explore their activity and stereoselectivity using a panel of structurally diverse cyclic imines as substrates...
August 13, 2018: ChemCatChem
https://www.readbyqxmd.com/read/30263082/oxa-michael-addition-to-%C3%AE-%C3%AE-unsaturated-nitriles-an-expedient-route-to-%C3%AE-amino-alcohols-and-derivatives
#6
Beibei Guo, Douwe S Zijlstra, Johannes G de Vries, Edwin Otten
Water addition to α,β-unsaturated nitriles would give facile access to the β-hydroxy-nitriles, which in turn can be hydrogenated to the γ-amino alcohols. We have previously shown that alcohols readily add in 1,4-fashion to these substrates using Milstein's Ru(PNN) pincer complex as catalyst. However, attempted water addition to α,β-unsaturated nitriles gave the 3-hydroxynitriles in mediocre yields. On the other hand, addition of benzyl alcohol proceeded in excellent yields for a variety of β-substituted unsaturated nitriles...
July 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/30147804/bench-stable-n-heterocyclic-carbene-nickel-precatalysts-for-c-c-and-c-n-bond-forming-reactions
#7
Felix Strieth-Kalthoff, Ashley R Longstreet, Jessica M Weber, Timothy F Jamison
Herein, we introduce a new class of bench-stable N -heterocyclic carbene (NHC) nickel-precatalysts for homogeneous nickel-catalysis. The nickel(II) complexes are readily activated to Ni0 in situ under mild conditions, via a proposed Heck-type mechanism. The precatalysts are shown to facilitate carbonyl-ene, hydroalkenylation, and amination reactions.
July 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/30069248/correlative-multiscale-3d-imaging-of-a-hierarchical-nanoporous-gold-catalyst-by-electron-ion-and-x-ray-nanotomography
#8
Yakub Fam, Thomas L Sheppard, Ana Diaz, Torsten Scherer, Mirko Holler, Wu Wang, Di Wang, Patrice Brenner, Arne Wittstock, Jan-Dierk Grunwaldt
Tomographic imaging of catalysts allows non-invasive investigation of structural features and chemical properties by combining large fields of view, high spatial resolution, and the ability to probe multiple length scales. Three complementary nanotomography techniques, (i) electron tomography, (ii) focused ion beam-scanning electron microscopy, and (iii) synchrotron ptychographic X-ray computed tomography, were applied to render the 3D structure of monolithic nanoporous gold doped with ceria, a catalytically active material with hierarchical porosity on the nm and μm scale...
July 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/30069247/tailored-mutants-of-phenylalanine-ammonia-lyase-from-petroselinum-crispum-for-the-synthesis-of-bulky-l-and-d-arylalanines
#9
Alina Filip, Emma Z A Nagy, Souad D Tork, Gergely Bánóczi, Monica I Toşa, Florin D Irimie, László Poppe, Csaba Paizs, László C Bencze
Tailored mutants of phenylalanine ammonia-lyase from Petroselinum crispum ( Pc PAL) were created and tested in ammonia elimination from various sterically demanding, non-natural analogues of phenylalanine and in ammonia addition reactions into the corresponding ( E )-arylacrylates. The wild-type Pc PAL was inert or exhibited quite poor conversions in both reactions with all members of the substrate panel. Appropriate single mutations of residue F137 and the highly conserved residue I460 resulted in Pc PAL variants that were active in ammonia elimination but still had a poor activity in ammonia addition onto bulky substrates...
June 21, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29937944/cooperative-surface-particle-catalysis-the-role-of-the-active-doughnut-in-catalytic-oxidation
#10
Thierry K Slot, David Eisenberg, Gadi Rothenberg
We consider the factors that govern the activity of bifunctional catalysts comprised of active particles supported on active surfaces. Such catalysts are interesting because the adsorption and diffusion steps, which are often discounted in "conventional" catalytic scenarios, play a key role here. We present an intuitive model, the so-called "active doughnut" concept, defining an active catalytic region around the supported particles. This simple model explains the role of adsorption and diffusion steps in cascade catalytic cycles for active particles supported on active surfaces...
May 24, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29861792/ring-expanded-n-heterocyclic-carbenes-for-copper-mediated-azide-alkyne-click-cycloaddition-reactions
#11
Filip Sebest, Jay J Dunsford, Matthew Adams, Jeremy Pivot, Paul D Newman, Silvia Díez-González
A series of well-defined copper(I) complexes bearing ring-expanded N-heterocyclic carbene (NHC) ligands has been applied to the azide-alkyne cycloaddition reaction. The obtained results notably showed that the six-membered NHC ligands outperform well-established five-membered ones. [CuI(Mes-6)] displayed a remarkable catalytic activity while respecting the strict criteria for click reactions.
May 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29780435/photoelectrocatalytic-synthesis-of-hydrogen-peroxide-by-molecular-copper-porphyrin-supported-on-titanium-dioxide-nanotubes
#12
Dogukan H Apaydin, Hathaichanok Seelajaroen, Orathip Pengsakul, Patchanita Thamyongkit, Niyazi Serdar Sariciftci, Julia Kunze-Liebhäuser, Engelbert Portenkirchner
We report on a self-assembled system comprising a molecular copper-porphyrin photoelectrocatalyst, 5-(4-carboxy-phenyl)-10,15,20-triphenylporphyrinatocopper(II) (CuTPP-COOH), covalently bound to self-organized, anodic titania nanotube arrays (TiO2 NTs) for photoelectrochemical reduction of oxygen. Visible light irradiation of the porphyrin-covered TiO2 NTs under cathodic polarization up to -0.3 V vs. Normal hydrogen electrode (NHE) photocatalytically produces H2 O2 in pH neutral electrolyte, at room temperature and without need of sacrificial electron donors...
April 24, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29780434/engineered-sulfur-resistant-catalyst-system-with-an-assisted-regeneration-strategy-for-lean-burn-methane-combustion
#13
Niko M Kinnunen, Matthew Keenan, Kauko Kallinen, Teuvo Maunula, Mika Suvanto
Catalytic combustion of methane, the main component of natural gas, is a challenge under lean-burn conditions and at low temperatures owing to sulfur poisoning of the Pd-rich catalyst. This paper introduces a more sulfur-resistant catalyst system that can be regenerated during operation. The developed catalyst system lowers the barrier that has restrained the use of liquefied natural gas as a fuel in energy production.
April 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29780433/influence-of-metal-deposition-and-activation-method-on-the-structure-and-performance-of-carbon-nanotube-supported-palladium-catalysts
#14
Wouter S Lamme, Jovana Zečević, Krijn P de Jong
The effects of the metal deposition and activation methods on metal particle size and distribution were investigated for carbon nanotube supported Pd catalysts. The Pd precursor was loaded by incipient wetness impregnation, ion adsorption, and deposition precipitation and was activated by thermal treatment under a nitrogen atmosphere or in the liquid phase by reduction by formaldehyde or sodium borohydride. Regardless of the metal precursor loading method, activation under a N2 atmosphere at 500 °C led to homogeneously distributed 4 nm Pd particles...
April 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29731952/the-strong-%C3%AE-cf-3-shielding-effect-in-hexafluoroisopropanol-and-100-other-organic-solvents-revisited-with-17-o-nmr-spectroscopy
#15
Annika Bernhardt, Harald Kelm, Frederic W Patureau
An 17 O NMR spectroscopy survey of more than 100 ubiquitous organic solvents and compounds, including some typical oxofluorinated solvents such as hexafluoroisopropanol, trifluoroethanol, trifluoroacetic acid, and others, is presented with D2 O as a reference. A strong alternating α,β-CF3 -substituent chemical shift effect was thus observed. This alternating deshielding-shielding effect is suspected to have a role in the exceptional properties of these oxofluorinated solvents, notably in oxidative cross-coupling reactions...
April 9, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29610628/selective-catalytic-oxidation-of-cyclohexene-with-molecular-oxygen-radical-versus-nonradical-pathways
#16
Ilse M Denekamp, Martijn Antens, Thierry K Slot, Gadi Rothenberg
We study the allylic oxidation of cyclohexene with O2 under mild conditions in the presence of transition-metal catalysts. The catalysts comprise nanometric metal oxide particles supported on porous N-doped carbons (M/N:C, M=V, Cr, Fe, Co, Ni, Cu, Nb, Mo, W). Most of these metal oxides give only moderate conversions, and the majority of the products are over-oxidation products. Co/N:C and Cu/N:C, however, give 70-80 % conversion and 40-50 % selectivity to the ketone product, cyclohexene-2-one. Control experiments in which we used free-radical scavengers show that the oxidation follows the expected free-radical pathway in almost all cases...
March 7, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29610627/colloidal-au-catalyst-preparation-selective-removal-of-polyvinylpyrrolidone-from-active-au-sites
#17
Baira Donoeva, Petra E de Jongh
Colloids with controlled dimensions, morphology and composition can be used to obtain supported metal catalysts with desired characteristics. Yet, removal of capping agents which block active metal sites in such catalysts can be challenging: mild methods often result in incomplete removal of capping agents, whereas harsher methods can cause change in particle size or morphology or cause metal segregation for bimetallic particles. Here we provide evidence that polyvinylpyrrolidone used as a stabilizing agent for gold colloids is present both on the metal and the support surface after colloid deposition on the TiO2 support...
March 7, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29541255/hydrogenation-of-lactic-acid-to-1-2-propanediol-over-ru-based-catalysts
#18
Kaituo Liu, Xiaoming Huang, Evgeny A Pidko, Emiel J M Hensen
The catalytic hydrogenation of lactic acid to 1,2-propanediol with supported Ru catalysts in water was investigated. The influence of catalyst support (activated carbon, γ-Al2 O3 , SiO2 , TiO2 , and CeO2 ) and promoters (Pd, Au, Mo, Re, Sn) on the catalytic performance was evaluated. Catalytic tests revealed that TiO2 yields the best Ru catalysts. With a monometallic Ru/TiO2 catalyst, a 1,2-propanediol yield of 70 % at 79 % lactic acid conversion was achieved at 130 °C after 20 h reaction. Minor byproducts of the hydrogenation reaction were propionic acid, ethanol, 1-propanol, and 2-propanol...
February 21, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29541254/exceptionally-efficient-and-recyclable-heterogeneous-metal-organic-framework-catalyst-for-glucose-isomerization-in-water
#19
Ryan Oozeerally, David L Burnett, Thomas W Chamberlain, Richard I Walton, Volkan Degirmenci
Heterogeneous catalysts are desired for the conversion of glucose, the most abundant sugar in renewable biomass, but presently their synthesis requires highly toxic chemicals with long synthesis times. We report the conversion of glucose into fructose and 5-hydroxymethylfurfural on a heterogeneous catalyst that is stable and selective and operates in the most environmentally benign solvent, water. We used a bifunctional solid with Lewis and Brønsted acid sites by partially replacing the organic linker of the zirconium organic framework UiO-66 with 2-monosulfo-benzene-1,4-dicarboxylate...
February 21, 2018: ChemCatChem
https://www.readbyqxmd.com/read/29515675/hydrogen-borrowing-alcohol-bioamination-with-coimmobilized-dehydrogenases
#20
Wesley Böhmer, Tanja Knaus, Francesco G Mutti
The amination of alcohols is an important transformation in chemistry. The redox-neutral (i.e., hydrogen-borrowing) asymmetric amination of alcohols is enabled by the combination of an alcohol dehydrogenase (ADH) with an amine dehydrogenase (AmDH). In this work, we enhanced the efficiency of hydrogen-borrowing biocatalytic amination by co-immobilizing both dehydrogenases on controlled porosity glass FeIII ion-affinity beads. The recyclability of the dual-enzyme system was demonstrated (5 cycles) with total turnover numbers of >4000 and >1000 for ADH and AmDH, respectively...
February 2018: ChemCatChem
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